Seating units having a pivotal, flexible, upper backrest element and/or a front, pivotal, flexible seat element are known to enhance the seating comfort when the user adopts different sitting postures.
Thus, U.S. Pat. No. 4,498,702 discloses a seating unit having a front seat element connected to the rest of the seat by means of two interspaced leaf springs maintaining the front seat element in an initial position. When the front seat element is loaded, it may flex downwardly to a maximum flexed position determined by means of a separate stop.
Furthermore, U.S. Pat. No. 4,603,904 discloses a seating unit comprising a lower backrest frame part formed of two upstanding frame members and an upper backrest frame part formed of two upstanding frame members arranged in continuation in the lower frame members. A flexible spring element is secured between the two pairs of the frame members to provide a flexing of the upper backrest frame part and thus of the backrest relative to the lower backrest frame part. Each flexible spring element comprises a plastic strut provided with a centrally arranged wire and maintaining the strut under compression and limiting the elongation thereof, when the backrest is loaded during use of the seating unit.
Finally, U.S. Pat. No. 4,869,552 and U.S. Pat. No. 5,039,163 both disclose a seating unit of the above type except that the flexible spring elements between the two backrest parts each comprises a leaf spring whose opposite ends are fixed to each their own U-shaped holder members at the inner end thereof, one open end thereof facing toward the other. At the open ends the holder members are provided with restrictive flanges extending laterally outwardly and adapted to interengage to define the maximum flexed position between the two backrest frame parts.